1. Field of the Invention
The invention relates to a planar mode converter used in printed microwave integrated circuits, and more particularly, to a planar mode converter with low transmission losses and a simple fabrication process, utilized for printed microwave integrated circuits.
2. Description of the Related Art
Coupled with the flourishing of wireless communication during the recent years, printed integrated circuits with characteristics such as small in size, light in weight, low production cost and adapted to mass production, have become one of the important techniques in the fabrication of communication modules. However, confronting with wireless communication systems in which microwave and millimeter bands are applied, planar printed circuits, such as microstrips and coplanar waveguides, the shortcoming of the planar printed circuit technique due to comparatively larger transmission losses is explicitly exposed. Therefore, for radio front-end modules that are getting more and more stringent and complex day by day, it is an arduous challenge to depend solely on conventional microwave and millimeter wave planar printed circuit techniques in the fabrication process. Hence, in order to minimize energy consumption and enhance system performance, non-radiative dielectric (NRD) guides and rectangular waveguides are widely used to replace certain planar printed integrated circuits and are applied to millimeter wave or higher bands because of their low transmission losses property, thus becoming one of the main-stream guiding structures for high performance band modules. During the past twenty years, Yoneyama et al. have invented the non-radiative dielectric(NRD) guide 10 by inserting a dielectric strip 13, represented as the rectangular dielectric rod 13 in FIG. 1 into a parallel-plate metal waveguide 11 so that signals are propagated in the dielectric rod without radiating energy. Yoneyama et al. in the meanwhile analyzed the characteristics of non-radiative dielectric guide and derived numerous related applications, including transmitter-receiver modules and array antennas.
Referring to FIG. 2, as another application structure that has low power losses and has been proficiently used, as disclosed in the U.S. Pat. No. 6,127,901, a rectangular waveguide 20 is shown. However, its structure is non-planar and therefore many interface converters are developed so that the rectangular waveguide 20 can be integrated with planar active or passive components. For instance, a planar microstrip 21 in FIG. 2 is integrated with the rectangular waveguide 20 by a square aperture 22. The known converters in the present time are classified into four categories below:
1. A broadband coplanar-strips quasi-yagi antenna similar to outdoor television antennas is made by using a printed circuit board, which is then inserted into the E-plane of the metal waveguide. The radiation pattern of the antenna is then able to correspond with the pattern of the dominant mode (TE10) of the rectangular waveguide, in a way that the energy is propagated by the dominant mode of the waveguide instead of the microstrip. The antenna has been disclosed both in xe2x80x9cA systematic optimum design of waveguide-to-microstrip transition,xe2x80x9d IEEE trans. Microwave Theory Tech., vol. 45, no.5, May 1997, written by H. B. Lee and T. ltoh, and xe2x80x9cA Broad-band microstrip-to-waveguide transition using quasi-yagi antenna,xe2x80x9d IEEE trans. Microwave Theory Tech., vol. 47, no. 12,pp. 2562-2567, December 1999, written by N. Kaneda, Y. Qian and T. ltoh,. The disclosures are incorporated herein by reference.
2.A patch antenna made by using printed circuit board is placed upon the E-plane of the rectangular waveguide. Then, the propagation energy on the microstrip is coupled into the rectangular waveguide by implementing the aperture-coupling concept so that the patch antenna radiates and further stimulates the dominant mode of the rectangular waveguide, thus completing the mode conversion. The antenna has been disclosed both in xe2x80x9cMicrostrip-to-waveguide transition compatible with MM-wave integrated circuits,xe2x80x9d IEEE trans. Microwave Theory Tech., vol. 42, no.9,pp. 1842-1843, September 1994, written by W. Grapher, B. Hudler and W. Menzel, and xe2x80x9cWaveguide-microstrip transmission line transition structure having an integral slot and antenna coupling arrangement,xe2x80x9d U.S. Pat. No. 5,793,263 1996, written by D. M. Pozar. The disclosures are incorporated herein by reference.
3. A microstrip probe made by using printed circuit board is inserted into the E-plane of the rectangular waveguide about a quarter of the wavelength in depth. Then, the ground plane of the microstrip probe is connected to the ground metal wall of the rectangular waveguide, thus achieving the mode conversion. The antenna has been disclosed in xe2x80x9cSpectral-domain analysis of E-plane waveguide to microstrip transitions,xe2x80x9d IEEE Trans. Microwave Theory Tech., vol. 37, pp. 388-392, February 1989, written by T. Q. Ho, and Y. C. Shih, which is incorporated herein by reference.
4. A microstrip made by using printed circuit board is connected to a ridged waveguide, and full-wave analysis is performed to design an impedence matching circuit between the microstrip and the ridged waveguide so that the microstrip mode can be converted into the waveguide mode. The antenna has been disclosed in xe2x80x9cA New Rectangular Waveguide to Coplanar Waveguide Transition,xe2x80x9d IEEE MTT-S Int. Microwave Symp. Dig., Dallsa, Tex., vol.1, pp.491-492, May 8-10, 1990, written by G. E. Ponchak and R. N. Simons, which is incorporated herein by reference.
As a conclusion drawn from the above, non-radiative dielectric guides, metal rectangular guides, with the aid of the transformation circuits are indeed able to demonstrate considerable outstanding low-loss characteristics. Nevertheless, all of the structures are three-dimensional instead of planar with complicated design, fabrication difficulty and expensive cost; these factors cause difficulties when interfaced with the planar printed circuit. In addition, due to different fabrication processes required by waveguide and planar printed circuits used, fabrication complexity issues arise during the construction of the entire circuit module. Consequently, it is laborious to make adjustments causing the production cost increase significantly and therefore inappropriate for mass production.
For the past few years, to captivate a larger communication market, wireless communication integrated circuits, which are light in weight with low profile and artistic in appearance, are prone to become the trend in the future.
However, as deduced from above, the main drawbacks of these mode converters currently available handicap the integrations of the integrated circuits since complicated fabrication processes are involved.
The invention relates to a planar mode converter used in a printed microwave integrated circuit; it includes a rectangular waveguide, a microstrip feed-in circuit and a microstrip feed-out circuit.
One object of the invention is to realize the feed-in/feed-out mode converter, the rectangular waveguide, and microstrip coupling in one unified fabrication process, and achieve mode conversion by utilizing electromagnetic coupling of the microstrip.
Another object of the invention is to utilize the feed-in/feed-out mode converter of the microstrip coupling to design and create a rectangular waveguide band filter.
The interior of the rectangular waveguide is filled with a plurality of dielectric layers which are closely adhered on top of one another, wherein the top surface of the uppermost layer, the bottom surface of the lowermost layer, and the right and left sides of the dielectric layers, are covered with metal materials. The lowermost dielectric layer usually has largest dielectric constant and thickness. Except for the lowermost dielectric layer, each dielectric layer has a rectangular aperture at its front-end and back-end, respectively. The rectangular apertures at the front-end are closely situated on top of another, and those of the back-end are also situated in the same manner.
The microstrip feed-in circuit is composed of a first metal strip, a second metal strip, a third metal strip and a feed-in metal ground plane. The first metal strip and the feed-in metal ground plane form a feed-in signal line, and the second metal strip is tapered in shape. The width of the first metal strip is the same as that of the narrow end of the second metal strip, and the narrow end of the second metal strip is connected with the first metal strip. The width of the third metal strip approximates to that of the rectangular waveguide, and the width of the third metal strip is the same as that of the wide end of the second metal strip. The wide end of the second metal strip is connected with one end of the third metal strip whose the other end extends partially into the front-end of the rectangular waveguide. Also, the extended third metal strip is situated closely on top of one another with the rectangular apertures at the front-end, and is electrically insulated from surrounding metal planes of the rectangular waveguide. The first metal strip, the second metal strip, and the third metal strip are adhered to the top surface of the lowermost dielectric layer, whereas the feed-in metal ground plane is adhered to the bottom surface of the lowermost dielectric layer.
The microstrip feed-out circuit is composed of a fourth metal strip, a fifth metal strip, a sixth metal strip, and a feed-out metal ground plane. The sixth metal strip and the feed-out metal ground plane form a feed-out signal line. The shape of the fourth metal strip is identical to that of the third metal strip, the shape of the fifth metal strip is identical to that of the second metal strip, and the shape of the sixth metal strip is identical to that of the first metal strip. The narrow end of the fifth metal strip is connected with the sixth metal strip, and the wide end of the fifth metal strip is connected with one end of the fourth metal strip whose the other end extends partially into the back-end of the rectangular waveguide. Also, the extended fourth metal strip is situated closely on top of one another with the rectangular apertures at the back-end, and is electrically insulated from surrounding metal planes of the rectangular waveguide. The fourth metal strip, the fifth metal strip, and the sixth metal strip are adhered to the top surface of the lowermost dielectric layer, whereas the feed-out metal ground plane is adhered to the bottom surface of the lowermost dielectric layer.
The advantages of the invention are as the following:
1. Relative to prior large and bulky mode converters, the planar mode converter of the invention is comparatively small in size with simple design and easy fabrication process.
2. By implementing a single unified fabrication process, in which a mode converter inclusive of feed-in/feed-out circuits and a rectangular waveguide can be formed, the mode converter thus has planar characteristics so that further integration with other microwave or millimeter wave integrated circuits can be accomplished more smoothly and compact. This then contributes to greater simplification in fabrication and lower production cost when designing multi-function radio-frequency modules.